Selective control circuit for alarm systems



May 16, 1933. M. w. MUEHTER 1,909,212

SELECTIVE CONTROL CIRCUIT FOR ALARM SYSTEMS Filed March 11, 1930 ELJJT-f (7 29 2g 53 OPEN Patented May 16, 1933 UNITED STATES PATENT OFFICE MANFRED MUEHTER, OF BROOKLYN, NEW YORK, ASSIGNOR TO SIGNAL ENGINEER- ING AND MANUFACTURING COMPANY, OF NEW YORK, N. Y., A CORPORATION OF MASSACHUSETTS SELECTIVE CONTROL CIRCUIT FOR ALARM SYSTEMS Application filed March 11, 1930. Serial No. 434,841.

The present invention relates to a control circuit for alarm systems particularly of the closed circuit fire alarm type in which the alarm bells are adapted to be rung either continuously, or in accordance with a code, upon the interruption of the normally closed circuit through any one of a number of alarm station boxes.

In addition to the alarm bells employed in a system of the above described type, the system 7 usually also provides a so-called trouble bellor other indicating device which is adapted to be sounded, or energized, when there is any trouble in the system such as would be caused by an open wire, or ground. The purpose of such a trouble signal is to indicate to the person responsible for the care of the installation that there is an open wire, or ground, somewhere on the system so that the trouble will be remedied at the earliest opportunity.

While such trouble indicating devices have been heretofore employed for fire alarm systems, prior installations of the closed circuit type have operated in such a manner that upon the occurrence of trouble, the signal alarm devices would be sounded simultaneously with the energization of the trouble indicator, in other words, sound a false alarm; Obviously, such premature operation of the alarm signals is undesirable under any conditions, particularly in a fire alarm installation for a school where the sounding of a false alarm might well lead to confusion. Furthermore, fire alarm systems of the closed circuit type have also been open to the objection that the trouble indicating device is energized upon the sounding of the alarm signals, which in some cases may be undesirable.

According tothe present invention, the above described objectionable characteristics are completely eliminated by providing a selective control circuit in which the energization of the trouble indicator is rendered independent of the energization of the alarm circuit, so that only the trouble indicator will be energized upon the occurrence of an open circuit, or ground, on the system. Furthermore, my improved control circuit is so arranged that the trouble indicator will not be energized upon sounding the alarm signals in the customary manner by breakmg the circuit at one of the box stations. The above and other advantageous features of the invention will hereinafter more fully appear with reference to the accompanying drawing in which- Fig. 1 is a diagrammatic view illustrating a fire alarm system embodying my invention in its normal inoperative position.

Fig. 2 is a diagrammatic view illustrating the sounding of the alarm bells upon operating a box station in the usual manner.

Fig. 3 is a diagrammatic view illustrating the energization of the trouble indicator upon the occurrence of an open wire, or ground, on the system.

Like reference characters refer to like parts in the different figures.

Referring first to Fig. 1, the system is shown with a simplified circuit in order to facilitate an understanding of the invention, it being readily apparent that additions and modifications maybe made to the apparatus shown, without departing from the invention. As an illustrative embodiment of the invention, the system is shown as comprising a series of gongs 1, 1 which are distributed at various points, one end of the gong circuit being connected to one of two supply mains 2 which are adapted to be energized from a suitable source of alternating current energy, not shown, through a switch 3. The other end of the circuitthrough the gongs 1 is connected to a stationary contact 4 forming part of a relay device, generally designated by the reference character 5. The gong relay 5 provides a second stationary contact 6 connected to the other supply main 2 and a circuit is adapted to be established between the stationary contacts 4 and 6 bymean's of a bridging member 7 carried by the movable armature 8 of the relay 5. As shown in Fig. 1, the armature 8 is held attracted by an energized winding 9, so as to maintain the bridging member 7 out of engagement with the contacts 4 and v6, thus maintaining the lineno conm M m P oi winding 0 of the l lie; e P21! 1M0 {.18

g n t 1 {Q "em' end when the erhe. -l1ie ettrectcd bythe 7 1e mm 14 main- K b r t wh i e switch in'the oppoeed conductor v H cult throughtilthe stetion to such en e'xtentne ermetm'elfi of reley 1 dgpelbeck total!!! I the eelecti reee w 27 of a type customeril em loyed in tire elerm etetione. No ly, e switch 27 is cloud to permit the flow of current through conductor hut ehculd the Jtetion' 9 be operate}! fer; the purpoee oi acundmg e g theewitch27will o -The&. I

is'con noes end two eneler ee y conductor-em end connected to 1 211}; ddl'vefezihds of legainduetance all 28. can an ecoi rovieeetepet is concedes over the line 28 to the 'ugction 80 leading to the rele. windin'gs 5 end 19, respectively. 1th the switch 27 of eech station it closed which is the normal condition of efl'eire it up obvious thet current will flow, in o poeite directions branches 0 each inductence coil 26 end eince the te 29 leedi the coil, ie at themi dle goint elect, the two portions of the coil 2 will balance each other and rmit alternating current to flowuelly t rough the conductors 26a E being very smell.

However, should the switch 27 of my one of the station; 24 be openecLes mu breakin; the glue at the etetion ior of 'ng" en elem, nt ml ow throughvone side only of coil 98 28b thereb the cury unhel opening nthe switch 27 the conductor.

tie the mt. inventmn pom em functional to prevent armature beckwhen eoundi .ef the clean gong: The l a rinciple underlying "resulting impedence of coil 28.

we F" .91. me, ee p ngnmenheelective in ectien, whif lieo tion of a circuit arrangement embodying my invention resides in the simultaneous use of both alternating current and direct current for the purpose of supervising the alarm box circuit. As indicated in the drawings, one possible way of obtaining this effect is by employing 1n the box circuit a rectifier 31 of the one-wa type such as the so-called cuprous oxide rectifier which is an unsymmetrical conductor of electrical current, although obviously there are other ways of obtaining the same result. When employing a one-way rectifier 31, as indicated, the resulting supervisory current is direct current with alternating current superimposed thereon having the same frequency as that of the suppl mains 2, whereas a two-wa rectifier wou d furnish direct current wit alternating current of double frequency. Obviously, it would be possible to obtain the same result by eliminating the rectifier 31 and simultaneously supplying the mains 2 with both direct current and alternating current from suitable sources. In the diagrams, the solid arrowheads "indicate the flow of alternating current, while the open arrowheads indicate the flow of direct cur rent.

In order to provide for a selective control with both alternating current and direct current flowing simultaneously, the relays 11 and 13 are adapted to operate only on al-, ternating current and direct current, respectively. Since the winding 15 of the rela 11 is in series with the condenser 32, re ay 11 can be operated onl by alternating current, and since the winding 19 of relay 13 has a high impedance, alternating current will not energize the relay 13. On the other hand, the winding 19 offers a comparatively low resistance to the flow of direct current, so that the winding 19 will remain energized as long as direct current is flowing in the circuit.

When the alarm gongs 1 are to be sounded by breaking the circuit through a box station at a switch 27, as shown "in Fig. 2, it is evident that direct current will continue to flow throu h the conductor 26b in spite of the fact t at the unbalancing of the box circuit by the coil 28 chokes the flow of alternating current to such an extent as to deenergize the winding 15. This result is obtained owing to the fact that the ohmic resistance of the circuit is only increased'by twenty-five percent of the resistance of the whole coil 28, this resistance being only a very small percentage in comparison to the ohmic resistance of the complete circuit. Consequently, opening the box switch 27 does not materially effect the flow of direct current through the winding 19 of the relay 13, as indicated by the open arrowheads in Fig. 2. On the other hand, the unbalancing of the coil 28 by opening the switch 27 has a. great influence on the impedanceof the whole circuit, since the full inductance of one-half of the coil 28 is suddenly inserted into a circuit. which before the opening of a switch 27 was nearly non-inductive in character, owing to the complete balance obtained by alternating current flowin in equal amount through the identical half portions of each coil 28. Therefore, the winding-19 remains energized by the continued flow of unidirectional current therethrough when the gongs 1 are sounded for the alarm, and it is evident that the trouble bell 21 will not be energized. And, assuming that the alarm circuits are functionin pro rly, as indicated in Fig. 2, it is evi ent t at there will be no indication by the trouble bell 21 upon the normal sounding of an alarm.

Let it now be assumed that there is an o 11 wire in. the circuit between the box stations 24, as indicated at 33 in Fig. 3, so that the flow of current is entirely interrupted through the box circuit. When this occurs, both the windings 15 and 19 are simultaneously deener 'zedso that both armatures 14 and 17 drop ack, as indicated in Fig. 3, and obviously, the trouble bell 21 is sounded when the contact arm 22 engages the stationary contact 20. But the s' al ongs 1 are not sounded owing to the act t at the contact arm 18 carried by the armature 17 engages the contact 12 to establish aholding circuit for the windin 9 of 'the gong relay 5, as indicated by the fiieavy circuit lines in Fig. 3. Therefore, the signalgongs 1 will not be sounded to give a false alarm u n the occurrence of trouble in the system 8bviously the occurrence of a ground will result in the same condition of alfairs shown in Fig. 3 for since the windings 15 and 19 are connected to the grounded main 2 the voltage will fall so ow as to deener the winding 19 and again cause it to bot sound the trouble bell 21 and establish a hold circuit for the winding 9 to revent soun ing of the signal gongs 1. n order to insure that the contact arms 18 and 22 will engage the respective contacts 12 and before the contacts 4 and 6 are connected by armature 7 the relay 5 is so designed that its armature 7 has to fall farther than the armature 17 in order to engage the stationary contacts, this relation being indicated in Fig. 1. Consequently when windin 15 and 19 are simultaneously deenergize winding 9 is reenergized before the armature 7 en-' ga s contacts 4 and 6.

claim:

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law

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